his application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from my application entitled INK-JET PRINT HEAD filed with the Korean Industrial Property Office on Dec. 13, 2000 and there duly assigned Ser. No. 2000/75936
1. Field of the Invention
The present invention relates to an ink-jet printhead, and more particularly, to a bubble-jet type ink-jet printhead.
2. Description of the Related Art
The ink ejection mechanisms of an ink-jet printer are largely categorized into two types: an electro-thermal transducer type (bubble-jet type) in which a heat source is employed to form a bubble in ink causing ink droplets to be ejected, and an electro-mechanical transducer type in which a piezoelectric crystal bends to change the volume of ink causing ink droplets to be expelled.
Meanwhile, an ink-jet printhead having this bubble-jet type ink ejector needs to meet the following conditions. First, a simplified manufacturing procedure, low manufacturing cost, and high volume production must be allowed. Second, to produce high quality color images, creation of minute satellite droplets that trail ejected main droplets must be prevented. Third, when ink is ejected from one nozzle or ink refills an ink chamber after ink ejection, cross-talk with adjacent nozzles from which no ink is ejected must be prevented. To this end, a back flow of ink in the opposite direction of a nozzle must be avoided during ink ejection. Fourth, for a high speed print, a cycle beginning with ink ejection and ending with ink refill must be as short as possible. Fifth, a nozzle and an ink channel for introducing ink into the nozzle must not be clogged by foreign materials or solidified ink.
However, the above conditions tend to conflict with one another, and furthermore, the performance of an ink-jet printhead is closely associated with structures of an ink chamber, an ink channel, and a heater, the type of formation and expansion of bubbles, and the relative size of each component.
In efforts to overcome problems related to the above requirements, ink-jet print heads having a variety of structures have been proposed in U.S. Pat. Nos. 4,339,762; 4,882,595; 5,760,804; 4,847,630; and 5,850,241, European Patent No. 317,171, and Fan-Gang Tseng, Chang-Jin Kim, and Chih-Ming Ho, xe2x80x9cA Novel Micoinjector with Virtual Chamber Neckxe2x80x9d, IEEE MEMS ""98, pp. 57-62. However, ink-jet printheads proposed in the above patents and literature may satisfy some of the aforementioned requirements but do not completely provide an improved ink-jet printing approach.
Thus, due to the complicated structures of the conventional ink-jet printheads, the fabrication process is very complex and the manufacturing cost is very high. Furthermore, each ink channel having a complicated structure has a different fluid resistance to ink supplied to each chamber, which results in large differences in the amount of ink supplied to each chamber. Thus, this raises design concerns for adjusting the difference. Due to the complicated structures of the ink channel and ink chamber connected thereto, foreign materials may adhere to the ink channel and ink chamber or ink may solidify, which may not only cause an obstacle to supplying ink to the ink chamber but may also clog the ink channel or the nozzle rendering it unusable.
Meanwhile, an ink-jet printhead disclosed in U.S. Pat. No. 4,847,630 is constructed such that an annular heater surrounding each nozzle, from which ink is ejected, is formed in a nozzle plate, and a C-shaped isolation wall, one side of which is open, is disposed in the vicinity of the heater. The ink-jet print head printhead constructed such that the heater and the isolation wall are formed in the same nozzle plate is advantageous in reducing offset between the nozzle and the heater. However, heat loss due to the nozzle plate is large and the structure is complicated since the ink chamber formed by the isolation wall is provided for each nozzle.
To solve the above problems, it is an object of the present invention to provide a bubble-jet type ink-jet printhead having a simplified structure which is simple to manufacture, especially for high volume production.
It is another object of the present invention to provide a bubble-jet type ink-jet printhead which is capable of effectively preventing adhesion of foreign materials and ink solidification and clogging.
It is still another object of the present invention to provide a bubble-jet type ink-jet printhead which has a low manufacturing cost and a long lifetime.
It is still another object of the invention to provide a bubble-jet type ink-jet printhead having a self-cleaning function.
It is further an object of the present invention to provide an ink-jet printhead that ejects smaller ink droplets thus allowing for a high resolution print on a sheet of recording medium.
It is still further an object of the present invention to provide an ink-jet printhead that prevents a backflow of ink which would prevent the operation of one nozzle from affecting the operation of a neighboring nozzle.
It is also an object of the present invention to provide an ink-jet printhead that has a quick response rate and is capable of being operated at a high driving frequency.
It is still also an object of the present invention to provide an ink-jet printhead where upon applying power, a bubble is formed which coalesces at a center of the nozzle, preventing the formation of satellite droplets.
Accordingly, to achieve the above objectives, the present invention provides a bubble-jet type ink jet printhead having a substrate, a nozzle plate including a plurality of nozzles, which is fixed to the substrate by an adhesive layer, a plurality of concave portions formed on the substrate, each of which corresponds to each of the plurality of nozzles, a plurality of resistive layers formed along the bottoms of the plurality of concave portions, each resistive layer surrounding the central axis that passes through the corresponding nozzle, and a plurality of ink feed grooves formed opposite the plurality of nozzles at the bottom center portions of the concave portions, the ink feed grooves being aligned with each of the nozzles so that the central axis of the ink feed grooves coincides with respective ones of the central axis of each of the nozzles. A portion of each nozzle opposing the substrate has a diameter large enough to surround each resistive layer, and a vibration element is disposed on the bottom of the substrate. Furthermore, a plurality of ink inlets, the lower portions of which are widely open, connect with the plurality of ink feed grooves, respectively.
The resistive layer has a doughnut shape, one side of which is open, an omega shape, or a polygonal frame. Each resistive layer has resistance that varies at regular intervals. The resistance of the resistive layer is adjusted by the width or height of the resistive layer. Preferably, a thermal insulating layer is formed on the substrate, on top of which the resistive layer is formed. In particular, a protective layer for protecting the resistive layer is preferably formed on the resistive layer